The present invention relates to turbomachines, such as blowers, compressors, pumps and fans of the axial, semi-axial and radial type. The working medium may be gaseous or liquid.
More particularly, this invention relates to a turbomachine with at least one rotor, with the rotor comprising several rotor blades attached to a rotating shaft. At least one stator can exist, with the stator being provided with stationary stator blades. A casing can exist which confines the passage of fluid through the rotor and the stator in the outward direction.
The aerodynamic loadability and the efficiency of turbomachines, for example blowers, compressors, pumps and fans, is limited by the growth and the separation of boundary layers on the blades as well as on the hub and casing walls.
The state of the art only partly provides solution to this fundamental problem. While various concepts for the fluid supply on turbine blades exist, these are not transferable to turbomachines since they primarily serve for surface cooling, not for boundary layer energization. Concepts are known from compressor cascade experiments in which air is blown out from a pressurized chamber inside the blade to the blade suction side to energize the two-dimensional profile boundary layer. Related alternative solutions provide for direct passage of the fluid from the blade pressure side to the blade suction side. Additionally, for rotors, a concept exists for the supply of air on hub and casing via axially symmetrical slots to influence the wall boundary layers there. Finally, publications of research institutes exist showing concepts in which rotors are blown at by individual nozzles near the casing to favorably influence the radial gap flow there. Accordingly, the general concept of influencing the boundary layer by blowing in or supplying fluid is provided in the state of the start, but the known solutions are trivial and only partly effective.
FIG. 1 schematically shows the solutions known from the state of the art. The figure schematically shows a hub 11 and a casing 1 between which a fluid flow passes from the left-hand side, as indicated by the big arrow. Also shown is a blade 2, belonging either to a rotor 6 or a stator 5, with the visible area of this blade being the suction side. As indicated by the arrows, drafts exist for a local air supply at different points of the turbomachine. In the case of rotor and stator blading, as well as plane experimental blade cascades, it is known to blow in fluid on the blade suction side between the leading edge and approximately 60 percent of the profile depth via slots 4 to influence the two-dimensional profile boundary layer. Here, the necessary fluid enters the main flow path from a pressurized cavity inside the blade 2. In alternative solutions, the blade profile is divided to enable fluid to be supplied by direct passage from the blade pressure side to the blade suction side.
In the case of a rotor, it is known to supply fluid on the hub 11 and/or the casing 1 before or within the area of the forward 50 percent of the profile depth via an axially symmetrical slot 3 to influence the boundary layer on the wall. Additionally, for rotors with radial gap of the casing, concepts exist according to which fluid is locally blown in on the casing via a number of nozzles 3 protruding into the flow path to influence the gap flow of the rotor at discrete locations on the circumference.
Only one solution, which is not described herein, provides for removal on the blade suction side and reflow on another location of the same blade, viz. the blade tip.
Accordingly, the state of the art describes the following methods of fluid supply:    1.) by straight slots in the forward and middle area of the blade suction side on rotors and stators,    2.) by axially symmetrical, areally flush slots in hub and/or casing far before the blade trailing edge on rotors with radial gap of the casing,    3.) by a number of circumferentially distributed, protruding individual nozzles on the casing before rotors with radial gap of the casing.
Most of these concepts either are only partially geared to aerodynamically particularly problematic zones within the blade passage or are simply orientated to a two-dimensional profile envelopment, without considering the complex, three-dimensional aerodynamic processes in the side wall area (near the hub and the casing). Others are only of limited effectiveness, although they are geared to locally critical flow zones.
Usually, in the state of the art, auxiliary air with higher pressure is externally supplied. Only one Patent Specification provides for air supply via slots on a further downstream location of the turbomachine.
The above described state of the art is documented in writing in the following publications:
U.S. Pat. No. 5,690,473 (Turbine blade having transpiration strip cooling and method of manufacture)
U.S. Pat. No. 6,334,753 (Streamlined bodies with counter-flow fluid injection)
U.S. Pat. No. 2,870,957 (Compressors)
U.S. Pat. No. 2,933,238 (Axial flow compressors incorporating boundary layer control)
U.S. Pat. No. 5,480,284 (Self bleeding rotor blade)
In the state of the art, it is disadvantageous that the existing solutions are not highly effective and, in particular, are unfavorable with regard to the efficiency of the turbomachinery. Rather, the existing blow-in concepts are relatively primitive and provide for blowing-in fluid either on the blade suction side only or in combination with blowing-in fluid before or within the blade row via axially symmetric annular slots on the hub and/or the casing. Apparently, there is a lack of concepts for specifically influencing the flow in the rim-near area and for influencing the airfoil boundary layers in a radially variable way (in the direction of the blade height). A non-axially symmetrical fluid supply on the side walls before or within the bladed region or also on blade tips in the running gap is not taken into consideration, although it is particularly advisable to have influence on the side wall boundary layers at the problem origin. Specifically influencing the three-dimensional flow processes in the area of the blade ends (and the associated flow exchange in the direction of the blade height) is not taken into account in the existing concepts.